The instant invention relates to vibration dampers for pole structures. More particularly it is concerned with a pole vibration damper that constitutes an improvement over that shown and described in U.S. Pat. No. 3,612,222.
As indicated in the aforesaid patent and a literature article entitled "Damp Destructive Pole Vibration" by Ray C. Minor that appeared in the December, 1973 issue of the magazine "Electric Light and Power", wind induced vibrations unless compensated for can destroy lighting poles and like structures. There are various kinds of wind induced vibrations that must be controlled including in particular those of a relatively high frequency which induce vibratory oscillation at an intermediate or at the midpoint portion of the pole structure.
Other pole induced vibrations requiring corrective action involve those created by the mechanical transfer of motion and sound to the pole structure by the movement and sound of traffic in the vicinity of the pole structure.
Prior art dampers for light poles and similar structures have taken various forms such as the pendulum devices of U.S. Pat. No. 3,259,212; the oscillation damping devices of U.S. Pat. No. 3,174,589 and the inertia mass rod and holder tube of U.S. Pat. No. 3,612,222.
The instant damper is designed to be less susceptible than prior art pole dampers such as those of the above patents to falling into phase with the various pole vibrational resonant frequencies, while still remaining, however, relatively sensitive to multiple and varying pole vibrational changes resulting from changes in wind direction and velocities and changing patterns in the movement of surrounding traffic.
This is accomplished in the damper of the instant invention by the use of multiple doughnut shaped metal discs or weights vertically and loosely arranged in a unique fashion about a rod disposed in a housing attached to the pole.
As in the case of the damper of U.S. Pat. No. 3,612,222, the instant damper can be fitted to existing as well as new pole structures and it also can be readily concealed inside a hollow pole structure if this is required for either esthetic purposes or to avoid vandalism. The instant damper also constitutes an improvement over those disclosed in the prior art U.S. Pat. Nos. 2,051,954; 2,714,161; 2,960,189; 2,195,041; 3,923,414; 3,207,009; 3,259,212; 3,938,626 and British Patent No. 920,586.